"It provides clues that we can use to hone in on more specific underlying causes," Bilder said. "This is one more piece of the puzzle."
Expectant mothers are advised to take folic acid, a vitamin, to reduce the risk of spina bifida. Perhaps someday, such research will lead researchers to a similar intervention to reduce the risk of autism, she said.
Results of the study, "Maternal Prenatal Weight Gain and Autism Spectrum Disorders," were published Monday in the November edition of the journal Pediatrics.
Autism spectrum disorder is now suspected in 1 percent to 2 percent of the population.
One of 47 Utah children born in 2000 was diagnosed with autism and its spectrum of disorders, according to a Centers for Disease Control and Prevention study released last year. That's higher than the national average, one in 88, but the discrepancy may be explained by higher rates of diagnosis in Utah.
The study published Monday compared 128 children diagnosed with autism spectrum disorders and born in Salt Lake, Davis and Utah counties to 10,920 children of the same age and genders born in the same counties.
It also looked at 288 Utah children diagnosed with autism spectrum disorders whose families are taking part in a research study. It compared them to 493 siblings who do not have the disorder.
In both cases, there was an association between small differences in the amount of weight gain and autism spectrum disorder. Autism spectrum disorder was found more often in children born to mothers who gained 33.5 pounds during pregnancy than it was in children whose mothers gained 30.5 pounds, for instance.
"The findings were consistent between two completely different groups," Bilder said.
The research was possible in Utah because it has been tracking maternal weight gain since 1994, unlike most states, which began tracking it in 2003, she said. The data are collected in birth-certificate records kept by the state.
The study had one surprising result: Researchers found no connection between a mother's pre-pregnancy body mass index and the incidence of autism.
That contradicted previous studies.
Bilder and her colleagues would like to replicate the study in other states with more diverse populations.
"This is a big deal for us here in Utah," said Bilder, who is seeking funding for more research. "It's nice to know it's worthwhile to pursue this here in Utah."
Other authors of the study are Amanda V. Bakian, Joseph Viskochil, Erin A.S. Clark, Elizabeth L. Botts, Ken R. Smith, Richard Pimentel, William M. McMahon and Hilary Coon.
Harper Randall, medical director at the Utah Department of Health's family health and preparedness division, said the study points to the importance of the Utah Registry of Autism and Developmental Disabilities, according to a U. news release.
"Utilizing this database," Randall said, "to study possible associations that may shed light on the causes of autism spectrum disorder is essential."
Guidelines for weight gain during pregnancy
University of Utah researchers say pregnant women should continue to follow their doctor's advice on weight gain during pregnancy. Here are the Institute of Medicine's recommendations, based on a woman's weight before pregnancy.
Healthy weight • gain 25 to 35 pounds
Underweight • gain 28 to 40 pounds
Overweight • gain 15 to 25 pounds
Obese • gain 11 to 20 pounds